1. Field of the Invention
The present invention relates to a photo printer for printing color images on roll paper, the roll paper being provided with yellow, magenta, and cyan heat-sensitive coloring layers.
2. Background Information
There are photo printers for printing color images on roll paper that is provided with yellow, magenta, and cyan heat-sensitive coloring layers. The following steps (1) to (5) are generally involved in printing color images.
(1) The heat sensitivity temperature for the thermal head is set to a first level, which is a temperature at which the yellow heat-sensitive coloring layer becomes colored, but the magenta and cyan heat-sensitive coloring layers do not become colored. This way, images in yellow are printed on the yellow heat-sensitive coloring layer in a printing region of the roll paper on which the current color image is to be printed.
(2) The yellow images printed in step (1) are exposed to the light of a yellow-fixing lamp.
(3) The heat sensitivity temperature for the thermal head is set to a second level, which is a temperature at which the magenta heat-sensitive coloring layer becomes colored, but the cyan heat-sensitive coloring layer does not become colored. This way, images in magenta are printed on the magenta heat-sensitive coloring layer in the printing region.
(4) The magenta images printed in step (3) are exposed to the light of a magenta-fixing lamp.
(5) The heat sensitivity temperature for the thermal head is set to a third level, which higher than the second level temperature. This way, images in cyan are printed on the cyan heat-sensitive coloring layer in the printing region.
The printing and exposure of images in steps (1) to (5) are performed while the roll paper is being conveyed. The printing region imprinted with the color images is cut off from the roll paper and ejected.
In this manner, yellow, magenta, and cyan images are thus printed in the printing region at different timings in an overlapping manner. The photo printer has a distal end detection sensor for detecting the distal end of the roll paper in order to prevent the images in the printing region from being offset in the conveyance direction of the roll paper. In a known photo printer, the distal end detection sensor is a reflection-type or transmission-type photo sensor disposed substantially in the widthwise middle of the conveyance path, such that the position of the roll paper in the conveyance direction is controlled based on the distal end detection timing, which the distal end detection sensor obtains by detecting the distal end of the roll paper.
The photo printer also has a side edge detection sensor for detecting a side edge of the roll paper in order to prevent printed images from becoming tilted due to slanted movement of the roll paper. The side edge detection sensor also prevents the printing images from being offset from one another in the main scanning direction (the width direction of the conveyance path), which is perpendicular to the conveyance direction of the roll paper. The side edge detection sensor includes a line sensor that is disposed so as to span the side edges of the roll paper being conveyed along the conveyance path. The line sensor determines as the border position of the roll paper the position between the light-receiving elements that detected the passage of the roll paper and the light-receiving element that did not detect the passage of the roll paper. In such photo printer, the main scanning direction position in which an image is to be printed with the thermal head is controlled based on the positions of the side edges of the roll paper detected by the side edge detection sensor.
In Japanese Laid-Open Patent Application No. 5-344295, position adjustment of roll paper in the main-scanning direction is performed by: reading with a scanner or other image-reading device a designated chart that has detection zones marked along the two sides of the roll paper; detecting a gap between the timing at which the line sensor detects the left side of the roll paper and the timing at which the line sensor detects the right side of the roll paper; and adjusting based on the gap in timings the position at which the line sensor starts reading the original image.
A conventional photo printer is disadvantageous, however, in that a distal end detection sensor and a side edge detection sensor need to be separately installed in the above-described manner, which increases the cost of the photo printer.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved photo printer that overcomes the above described problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.